Some time on Tuesday afternoon, about 50,000 Comcast Internet customers in Houston will become part of a massive public Wi-Fi hotspot network, a number that will swell to 150,000 by the end of June.

Comcast will begin activating a feature in its Arris Touchstone Telephony Wireless Gateway Modems that sets up a public Wi-Fi hotspot alongside a residential Internet customer’s private home network. Other Comcast customers will be able to log in to the hotspots for free using a computer, smartphone or other mobile device. And once they log into one, they’ll be automatically logged in to others when their devices “see” them.

Comcast says the hotspot – which appears as “xfinitywifi” to those searching for a Wi-Fi connection – is completely separate from the home network. Someone accessing the Net through the hotspot can’t get to the computers, printers, mobile devices, streaming boxes and more sitting on the host network.

Comcast officials also say that people using the Internet via the hotspot won’t slow down Internet access on the home network. Additional capacity is allotted to handle the bandwidth.

What’s interesting about this move is that, by default, the feature is being turned on without its subscribers’ prior consent. It’s an opt-out system – you have to take action to not participate. Comcast spokesman Michael Bybee said on Monday that notices about the hotspot feature were mailed to customers a few weeks ago, and email notifications will go out after it’s turned on. But it’s a good bet that this will take many Comcast customers by surprise.

If you have one of these routers and don’t want to host a public Wi-Fi hotspot, here’s how to turn it off.

• Look for a heading on the page for “Service Address.” Below your address, click the link that reads “Manage Xfinity WiFi.”

• Click the button for “Disable Xfinity Wifi Home Hotspot.”

• Click Save.

You can see screenshots of the process in the slideshow above. Note that this will only work once the hotspot is live on your router.

Some other details about the hotspots:

• Each hotspot actually contains separate connections for 2.4-GHz and 5-GHz Wi-Fi devices, and the Arris routers use the 802.11n standard.

• If you have one of the Arris modem/router combos, but are using your own Wi-Fi router, the Arris device won’t broadcast the free hotspot. Likewise if you are using your own modem as well as your own router.

• If you opt out of hosting a hotspot, you can still use others’ Xfinity Wi-Fi hotspots with your Comcast login.

• The additional capacity for public hotspot users is provided through a separate channel on the modem called a “service flow,” according to Comcast. But the speed of the connection reflects the tier of the subscriber hosting the hotspot. For example, if you connect to a hotspot hosted by a home user with a 25-Mbps connection, it will be slower than if you connect to a host system on the 50-Mbps tier.

• I asked Spencer Kurn, analyst and partner with New Street Research, whether Comcast Internet subscribers may be liable for illegal activities conducted by people using the hotspot associated with their accounts. Kurn said no, anymore than Starbucks is liable for illicit behavior by the customers who use its in-store hotspots.